giovedì 1 ottobre 2009



The head CT shows an approximately 2 cm mildly hyperdense mass in posterior fossa, slightly eccentric to left. There is mild hydrocephalus of lateral and third ventricles, with small 4th ventricle suggesting a 4th ventricle obstructing mass. The head MRI shows a mass arising from the 4th ventricle with mild increased T2 signal and enhancement. Extensive leptomeningeal thickening and enhancement.
The MRI of the cervical and thoracic spine shows complete encasement of spine cord (intradural, extramedullary) with abnormal enhancing soft tissue (“sugarcoating”). Abnormal increased T2 signal of entire cord compatible with myelomalacia.

Differential diagnosis
- Medulloblastoma
- Ependymoma
- Pilocytic astrocytoma
- Atypical teratoid/rhabdoid tumor

Diagnosis: Medulloblastoma

Key Points

WHO Grade IV PNET tumor
Comprises 15-20% of all pediatric tumors, 30-40% of all posterior fossa tumors (most common site)
1/3 will have subarachnoid metastatic disease at presentation
Presentation usually nonspecific: headache, ataxia, vomiting
Usually 6-11 years old, M>F by 2-4:1
Treated with combination of surgical excision and adjuvant chemotherapy

Radiologic overview of the diagnosis

Classically: Round dense mass arising from 4th ventricle (roof)
CT: Almost always hyper dense, 50% with cysts/necrosis, calcifications in 20%
Dilated lateral and 3rd ventricles secondary to obstruction

- T1WI = hypo intense to gray matter
- T2WI = isointense to gray matter
- DWI = restrictive diffusion
- T1 + Contrast = almost always enhancing, usually heterogenous
- Leptomeningeal and spinal metastasis are seen in up to 1/3 of disease, so MUST image entire spinal column

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